Tests and diagnosis

A thorough exam and appropriate diagnostic tests are essential for an accurate diagnosis. Research has suggested that drug allergies may be overdiagnosed and that patients may report drug allergies that have never been confirmed. Misdiagnosed drug allergies may result in the use of less appropriate or more expensive drugs.

Your doctor will conduct a physical examination and ask you questions. Details about the onset of symptoms, the time you took medications, and improvements or worsening of symptoms are important clues for helping your doctor make a diagnosis.

Your doctor may order additional tests or refer you to an allergy specialist (allergist) for tests. These may include the following.

Skin tests

With a skin test, the allergist or nurse administers a small amount of a suspect drug to your skin either with a tiny needle that scratches the skin, an injection or a patch. A positive reaction to a test will cause a red, itchy, raised bump.

A positive result almost always indicates a drug allergy. A negative result is more difficult to interpret because of differences in the reliability of tests. For some drugs, a negative test result usually means that you're not allergic to the drug. For other drugs, a negative result may not rule out the possibility of a drug allergy.

Blood tests

Your doctor may order blood work to rule out other conditions that could be causing signs or symptoms.

While there are blood tests for detecting allergic reaction to a few drugs, these tests aren't used often because of the relatively limited research on their accuracy. They may be used if there's concern about a severe reaction to a skin test.

Results of diagnostic workup

When your doctor analyzes your symptoms and test results, he or she can usually reach one of the following conclusions:

You have a drug allergy

You don't have a drug allergy

You may have a drug allergy — with varying degrees of certainty

These conclusions can help your doctor and you in making future treatment decisions.

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